{Kedei Kelipah is a term used in Kashruth for the amount of something that needs to be removed in order to allow one to treat the remnant as Kosher. (This only applies under certain conditions, which are outside the scope of this question - at least I happen to believe it is outside the scope of this question, but feel free to bring it into your answer if you think it is necessary.)}

What exactly is a Kedei Kelipah, and how big is it? How does one remove it, and how does one remove it if the item in question is very thin itself?

The piece that swallowed the issur has to be cut out in one piece without causing any crumbs this the definition of kdei klipah(see Schach siman 96:7,and Chachmas Adom klal 42:11 ,Kdei netilah is 2 centimeters(see Shulchan Aruch YD siman 105:4) for picture see sefer Basar Bechalav - Madrich Hilchati-Hebrew Halacha pg.42.